Automatic telephone system



June 26, 1928. 1,674,652

'c. E. LoMAx AUTOMATIC TELEPHONE SYSTEM Filed May 14 1921 4 Sheets-Sheet 1 l'nuan Elf- Elarsnua E'Lnmax June 26, 1928.

c. E. LoMAx AUTOMATIC TELEPHONE SYSTEM Filed May 14. 1921 4 Sheets-Sheet 2 -N.\\ M i q 2 1m Mimi mi W 14 m T M n W wmsQ h w fl w i m Q 3 W Q Hgg E w Ln L" NN R June 26, 1928. 1,674,652

C. E. LOMAX AUTOMATIC TELEPHONE SYSTEM Filed May 14 1921 4 Sheets-Sheet 3 Q 3 I q Q r8 lg zczskg Elar'efinca Elnmax 57w BITE:

June 26, 1928.

c. E. LOMAX AUTOMATIC TELEPHONE SYSTEM 4 Sheets-Sheet 4 File N MM km fi'nenii iii the fiiet se le'cfdr release Trek? fr Patented June 26, 1928. i

w NITE-STATE5 CLARENCE E. LOMAxOF CHICAGO, ILLINOIS, AssreN R, FYMESNE ASSIGNMEITTS, "rd AUTOMATIC ELECTRIC INC, OF CHICAGO, IIJIJINQTSFA CORPORATION OF DELAWARE.

A TOM TIC meLEi iiq n'h Cisiifimi.

. i' u'e t oii filed May 14,

The pi'esent inveiitioh relates general to automatic telephOhesy stems; but more es peciaily to, modern systen'is f the S alled tW wire type, in which the iilltoriizitie 5 switches ere controlled Over the t'WI'O side eof a. ceiling line in Series; and thefphjecfc;

broadly stated, is '60 ifnprdve the ci'r'cf i'i'tfs Of the switching mechanism it th e ex chz nge with a View prificipally tO' subst'itiitilig'pqeitivecircuib errahgernenjts {of performing certain necessary fflnetiOn s i'n place Of the eircuit armhgemeilt's Ordinarily u sed hf'etqfOre which depehd (in rela'yswhieh'zireslow to the present pracfii'clejfl eseleefior eiviteh'is provided With a-lineflr elayifoi controlling the OpeIetiOIi. Of the and" afslOW ad;-

lay and due to its slo ifrel eas in g character'- ietic it holds .up during ii 'o he itafry deepergizations of the line relay While theJSWlt-Qh is being Operated, holds the release magnet circuit Open, and lflfiifltaiIlS ,jground On the release trunk to pfOv'ide a hbldi'i g c'ii'cuit for the p iecechng, switch Or switches, As s O as zi second selectb l tru nk line is sel ec'te'l the switching relay p'ii'll's u p,'discdrir ect se the i1}- eoming line CbildfiCtOIS ffe'in the line relay and, extends them CO the linejreiay of the second selector, and Connects the incon'iirig Outgoing felea setrunk extendihg'to' the see- Ond i'eiectoia' Vhe tithe .l'i ri'f'eliiybf fihe first seie'cfor is c'lis co nn'ected it il'iffl'fidiqtlY falls hack and Opens the CiTiCLlit ofthe 510W acting release relay, but this relay, being slow YO deeneigize, does; not fall back it O ce but ihairitains the rel ees tri nk g'i'oui ded until grOLind is fed back from the second selector. This ojetirs \VhBIi ithe'lil' ef and release re'leysefuthe second selector' pull 11p 51H respensive be the eXtenSi'OI'y f the l'ine conductors and Ordinarily requireeO' fly ii 's'mall C entire igo'nnectioh depends Oh the .tinie P ifi ii i the 01 "iii M-J W i 1 11 :1113; "sh ijt m dixjxi hi 'eh is 'cbnn'eeted iO' the "release trunk tO pie le't iteld Winghn Pbelr lfiy S v co ii g release felayforeonfii'olling the;re1e%1se., back ddlfingimfiulse's "S, Vhf1e s econd' The latter relay is energized hjfthe line ree release t'iii i'ikhy Of the "test Wiper to fe ruiid 'wi 1'1'nOt be fed wea me {10 'fii'L a' ndf t '6 prese t tie-e e a 'hti fi renadi e t e preceding 's Q Whi e S lT Q is r fi 'n if Th sh ter- 0 1t sh i l'd' he stated, jender's felea'sie 's'o' m g t 'wi l 34 0b fit en rely 1 4 .i course, grOunp case the outgoing trunk line associated therewith is open any call received at the repeater will be locked up and an alarm will be sounded to notify the attendant.

Still other features of the invention relate to an improved control circuit for the line relay of a selector or connector switch, and

to an improved method of providing for the change over in a selector switch. The foregoing and other features not now specifically mentioned will be described hereinafter with reference to the accompanying drawings, in which there is illustrated by means of the usual circuit diagram su'tlicient of the apparatus in a telephone system embodying the invention to. enable the same to be explained and understood.

To facilitate the explanation of the various features a multi-Oflice telephone system has been assumed, and the drawings when laid out in order, with the corresponding lines at the ends thereof in alignment, show the apparatus which is required to extend a connection from a calling station A, Fig. 1, in one of the offices or exchanges of the system to a called station A, Fig. 41, in another ofiice orexchange of the system. This apparatus comprises the primary line switch P and the secondary line switch S, Fig. 1, the first selector D, and the outgoing secondary rotary line switch S Fig. 2, and the repeater B, Fig. 3, all of which are located in the origi nating exchange, together with the incoming selector E, Fig. 3, and the connector H, Fig. 1, which are located in the second exchange.

All of the switches, except for the novel circuit improvements introduced, are of well known construction and function and on this account will not be described in detail as to their mechanical operation. This applies also to the trunking arrangements, and to the equipment at the subscribers stations. Further details may be had if desired by referring to the book entitled Automatic Telephone Practice by Harry E. Hershey, third edition. 7

It may be stated, however, that the selector and connector switches in all ofiices are of the Strowger vertical and rotary type. In the originating exchange calling lines are extended to first selector switches by means of primary and secondary line switches of the Keith or plunger pre-selecting type. In the second oflice or exchange, in which the called line is located, the subscribers lines are provided with individual line switches of the rotary type.v These switches have access to relatively large groups of twenty-five trunk lines each, and consequentlysecondary line switches are not necessary. The interoflice trunk lines extending from the originating exchange to the second exchange, which are the onlyinter-o'tlice trunk lines shown, are all in a single group, this result being accomplished by the use of secondary line switches of the rotary type between the first selectors in the originating office and the outgoing trunk repeaters.

Proceeding now with the operation, the process of establishing the connection referred to extending from the calling station A, Fig. 1, to the called station A, Fig. 4, will now be explained, it being assumed that the telephone number at the called station is #2345. When the receiver is removed at the calling station a circuit is completed over the line conductors 11 and 12 for the line relay 16 of the primary line swi ch P. Upon attracting its arn'iatures 23 and 24: relay 16 closes parallel energizing-circuits through the pull down winding 17' and the holding winding 18. of the'line switch, both of these circuits including the lower low resistance winding of the line relay and the grounded conductor 25. This latter conductor, it may be mentioned, extends to ground through the left-hand winding. of supervisory relay 39 of the master switch M, and may be considered for all practimil purposes to be directly connected to ground inasmuch as the left-hand winding of relay 39 l1as a resistance of less than 1 ohm. 'The lower winding of the line relay 1G is also very low in resistance as stated. (about ohms preferably) and a heavy current i'lOW is at once established in the pull in winding 17, with the result that the cutoff armature 28 and the plunger arm 29 are both immediately operated, the former separating contact springs and 22 from contact springs 19 and 21, respectively, and the latter forcing the bank springs 30, 31, 32, and 33 into engagement with bank contacts 34, 35, 36, and 37, respectively. J-tlthough the initial energizing circuit for the line relay 16 is opened by the separation of the cut off springs controlled by armature 28 the line relay is not deenergizcd, but remainsloclted up by the circuits through its lower winding. By the engagement of bank springs 30 and 33 with the bank contacts 341 and 37 the line conductors of the calling line are extended through to the conductors and 53 of the trunk extending to the secondary line switch S. By the engagement of bank spring 32 with bank contact 36 the holding or cut-off winding 18 of the line switch. is connected lit with thcvrelease trunk col'nluctor '52 offlthe trunl'r'li ne extending to the secondary line switch S. 'This' holding winding now has its upper terminal connected to "groundby Way of armature 24and the lower winding of the line i'elay16', and ground potential is th tis placed upon conductor 52. A circiiit is thus completed over the'bran'ch conductor 27 extending to theina'ster sw tch bank contact upon which the master switch wiper is now resting for energizing the starting ref .lay of the master switch M. Upon energizing, relay 10 closes" ac-ircuit for the lock- Contacts'o f relay 42'. V p

about 300' o'h'ins and" is high enough to pre-v iii) ing magnet 41, which, unlocks 'tl'ieinaster switch shaft and thus brings about the realignment otall the idle line switch plungers in front of the next idle trunk line The locking relay 11 also closes a circuit for the open main relay 1-2 which, upon energizing, disconnects the conin'ion' conductor 26Troni the negative pole of the battery in order to prevent any of the line switches nomineingoperated until the master switch comes to rest. It will; be observed that there is a resistance 38 -which'is shunted around the This resistance is vent the "operation" of the line switches, while still furnishingenough curr'nt t'o maintain the line relay 16flocked u'p. The provision of this resistance isnotabsohitely necessary in all causes, since fthe line relay may remain locked "up over the circuit through theholdingf winding 18,Which not interrupted by the operation "of the master switch','-but th'is holding wi riding is of very high resistance;abolit 130C ohms, and theresistancef38 s added as a precautionary measure in order to insure the hold ing upot the line relay and in order-to elinr inate the 111e'ces'sityo'li careful It Wlll bej obsc rvedthat as soon-as the line relay energizes and-the circuit is coinplete d for the holding winding 18'," grouiidfpoten tial will be placed onthe private normal.

conductor 14;, which" extends to" multiply connected test contacts in the banks of the c e I H -11 connector switches which have access to the line of station A; Thisrenders a en-ring line busy and inaccessible to other calling lines. i i i 1 i i The operation of thesecondary line switch Stollows instantlya'l'ter the opera'tionof the primary line switch P and is broughtyabo nt b the en a ement of bank so 11111 .131 with y D h 1 a 71, 72, and 73 intoengagenient 'with the bank contacts 74:; 75. 76,and 77;, respectively! the engagement of bank springs 70, 72, *a'1'1d-73 with bank contacts 7 1, 76, and 77,

respectively, the conductors 50, 52v-and 53 of the trunk line incoming to the secondary ,l-ines'witch are extended into connectionwith the conductors 80,-"81, and 82 of the trunk line extending to the first'selector D. "By theengagernent ofba'nk spring 71'With' the ban'k'conta'ct "75 a circuit iscoinpleted'over conductor-63 and through them'aster swltch wiper to the startingrelay 64 of the secondary master switch, M; The starting re lay 64,,upon energizinggclo'ses afcircuit for the locking relay or inagnet 6'5, which unlocks the rnaste'i' switch. shaft and advances "the" plungers of all-the-idle line switches into position? 'opposite' the next idletrunk, li n'erf Theop'enmainrelay 66 is energized in parallel with the locking magnet "a'n'd jd iisconnects thecommon conductor; 62 from the negative pole of battery in order .tQPIB- vent-*the operation oifany ofthe secondary line swi tches while the i In'aste-r switch is in operation. I V 1 s v I 1 "lVhcn the callingvlineis extendedflto the firstsel'ector D, as described in the foregoing, the line relay-100 is-energized over the l'inecircnit anfdatits arinature-112 closes a circuit through the upper windingof the slow actingrelease relay 101. Upon eneri-l gizing, the latter relay prepares'acircuit-for the Vertical magnet 105 at 'its'armat-ure 118,

' prepares certain other circuits, which will be r 5 described, at its armature 114'; and, atarma ture 1 15" connects ground to the release truhk conductor81. Bythe latter operation a holding-circuit is completed for the holdj inding-"180i? 'the priimai y line switch P which inayhe traced hem grounded arma ture 127 of the switchingfrelay 104-by way of the'i'v'ork'ing contact otarniature 115 and thesaid armature, conductor 81, bank con- 'tactj"7(i, banksprin'g 72,; conductor v5?,bank

contact 36,; bank spring 32 and the holding wi'fK-ling"1'8 to battery. This circuit serves tofinia'intain the holding winding18 en'er gi'z'ed' throughoutthe connection. It-will be observednow'tha't since direct ground is supplied to the holding winding- 18 over this I new path, the lower winding, of the line re-H lay 16 will be short circuited, and the said relay will deenergrze; As soon 'as'armatures 23 and 24' are reatti'actgltl e locking circuit through the lower. winding of the line relay is permanently opened.

vThe callingsub'scriberlmay now proceed to' opeirate his-calling device in accordance with the fir'st di'gi tin the desirednumber.

A'sa result twoiiiterrupti'ons. are produced 7 in the circnitof' the line relay of the selector D and this relay is'deenergize twice momentarily, each'tijnie sending an inipiilse oitcurrent to the vertical magnet over the following circuit: From the grounded armature 128 by way of the resting contact of said armature, normally closed contact springs and 111, armature 113 and its working contact, armature 117 and its resting contact, and the winding of the vertical magnet 105 to battery. By the operation of the vertical magnet the switch shaft is raised two steps and the wipers 1.40, 141, and 142 are brought to rest opposite the second level of bank contacts. Although the energizing circuit 01'' the relay 101 is interrupted each time the line relay transmits an impulse to the vertical magnet, said relay does not fall back at this time on account of its slow releasing characteristic produced by the now short circuited lower winding. This wind ing is of low resistance, preferably about 25 ohms. At the first vertical step of the shaft the oil normal springs are shifted in the usual manner and by the closure of off normal springs 123 a circuit is completed for the stepping relay 103 which extends from the grounded armature 128 by way of the resting contact of saidarinaturo, the working contact of armature 114 and the said armature, armature 118 and its resting contact, ofi' normal springs 123 and the winding of relay 103 to battery. Upon energizing, relay 103 establishes a locking circuit for itself at its armature 120 over .a path which will be sufficiently obvious, and at its armature 119 prepares a circuit for the rotary magnet 106. The off normal. springs 122 are closed at the same time as springs 123 and by their engagement the high resistance relay 102 is connected in multiple with the upper winding of relay 101. It follows, therefore, that each time the line relay energizes following a momentary deenergization a current impulse will be transmitted through. the winding of relay 102, but this relay is of extremely high impedance and resistance (about 5000 ohms preferably) and does not operate during the vertical operation of the switch. At the end of the series of interruptions for the first digit in the number, the line relay 100 comes to rest in energized position and the circuit of relay 1.02 is permanently closed. Relay 102 is accordingly energized and at its armature 1.17 opens the circuit of the vertical magnet 105, while at armature 118 a circuit is closed for the rotary magnet 106 which extends from the grounded armature 128 by way of the resting contact oif'said armature, working contact 0t armature 114 and the said armature, armature 118 and its working contact, working contact of armature 119 and the said armature, and the winding of the rotary magnet 106 to battery. The rotary magnet is energized when its circuit is closed and by rotating the switch shaft one step brings the switch wipers into engagement with the first set oi bank contacts in the level. opposite which they were raised. At the same time the rotary magnet opens its interrupter contact and thus breaks the locking circuit of.

the stepping relay 103, which accordingly deenergizes and breaks the circuit of the rotary magnet, which then deenergizes also and again closes its interrupter contact.

The operation now depends upon whether the first trunk line is busy or idle. It this trunk line is busy there will be a ground po tential on the test contact with which the test wiper 141 is in engagement and a circuit will be completed by way of the said test wiper for again energizing the stepping relay 103. This relay is thus operated again and the rotary magnet operates likewise to advance the switch wipers into engagement with the next set of bank contacts, at the same time causing the stepping relay to de energize. This operation in which the step-- ping; relay and the rotary magnet are energized alternately will continue as long as the test wiper 141 continues to engage grounded or busy test contacts, but as soon as an idle trunk line is reached, which we will assume to be the trunk line xtending to the secondary rotary line switch Sflthe test wiper 141 will find no ground potential on the associated test contact, which is the test contact 144, and the stepping relay 103 will not again be energized. Instead, the switching relay 104, which has heretofore been short circuited, will be operated by current flow over a circuit which may be traced from the grounded conductor 81 by way of the winding ofthe switching relay 104, in-

terrupter contact of the rotary magnet- 106, oil normal springs 123 and the winding of the stepping relay 103 to battery. Upon en ergizing, relay 104 disconnects ground tron) Various circuit conductors in the selector at armature 128, connects the incoming release trunk conductor 81 to the test wiper 141 at armature126,'andj at armatures and 129 disconnects the conductors 80 and 82 of the trunk line from the windings of the line relay 100 and extends them by way of wipers and 142, hank contacts 143 and 145, and trunk line conductors 1.46 and 148 to the winding of the line relay 161 of the secondary line switch S and to ground, respectively. In. addition to the foregoing at its armature 127 the switching relay 104 removes the short circuit normally existing around the lower winding of the release relay 101. The slow acting characteristic of the relay is thus destroyed, and the relay remains locked to the holding circuit which includes the release trunk conductor 81, current being supplied to conductor 81 through the lower winding of relay 101 for maintaining relay 104 of the selector and the holding winding 18 of the primary line switch energized. As mentioned hereinbetore, the lower winding of relay 101i c1? lit) der the. ti iik liiiee e i'1d ing comparatively Low r eeistence, and the test Contact ll t u ntt its, iiihlhilglg in tile banks whe the the line is. ei eende'd 10' the e ecoiidery lines witch theili ie i'elay 161 at circuit lit its airline 1s titomu th'e' f ducter rty 'v\ y ing colit'z llct,

is energized ctclk time 167 which t e 'iOhnded relezys'e trunk ft J tlire 167f and its W0" tyi iciiiig the siyitchiiig relay 1 wv ildi e" 'of e tepping ixia'g eti' 1 2te t+ tei y Atthe sahie time the teetiyipei 181 t0 the ab e. c rcuit at a. pii t, midway between the eaiclijet' itching re ay the stepping iimgnefl this 60 ;196- tihl heiii-g estgeblieh ed at zli' lhgtttirle 1168.? T he operation nowfdepehd's upon hether the trim}; line with which the Wipefs of the secondary line switch are in engzt'gement is busy ei idle. If such trtink linei hliefy the test Contact eng gedby thetest Wip'ei'j 18 11 Will be Shoi-t ciicuitedea nd the "stepping hiagh'et 162 which interrupts its own circuit t'vill-"ztct 'zis a buzzer to eeveme the switch w'yipe'r's step by step 1n Search efnn dlet fnk hne; Thi's met emerit 01 11116 switch willfcojnthiue uiitil' eihtien (it thew-pet y magnet wi11 .cease,

at 1 60 be ng now" he l e-ng'eishort 'clr- Rt ciiited will eiieigize' at oijce'ih seiies with the rotary magnet, the latter"ren n HERBS/111761111?! to the high res stenceefi the switching iiei ziy I Upc lie nel gizing, eivitchfing rehiyf160 connects the release jtr'ljmk cointiltCtOI' 147 to the feet Wiper 181' at zti hituie- 165, thus Iii-Liking the seleeted trunk line buggy, establishes fat heldihg circuit for itself V at its mnmture 16 15 and at a i'niatiu'es 1133 and 166 disconnects thetriink conductors Mfitahd, 1 18 from the winding 01 the i'ehty 161 end from ground, iespectixiely, mid. 6R1'PI1C1'\J themhy titty 0f wij je fsi 1 80 182;

, bank contacts 183 aiid 185, 11-11mm i 1S6 "(141d 188, normally closed 30 V I e oi? the reversing; relay 205, andthe lefthand windings of the repeating,coilbat the r6 3 pester tothe upper and lewei"wlh dingsf le w e le e ay The cailiiig line having heeriextended t6 the line relay 200 Ofthe repleeter this relay eiiefgize'dv iii the usual 11121111161 and closes a circuit for" the siowecting releas relay 201, Upo energ zlng in turn relay 1 2 01ccmpletesii heldiiig-cincuit at its" armtime 213 which may he ti ececlihsfoilows;

From the grounded armature 21.3 byfwa'y' 1165 a n d the Said ari'netiu'e, release ti'i 670 are t e the t'riz ik liiie ning 111-,

'ductpfs Yew-ee 1 of the orking cqntect of sai'clei'matu e, release tru k co dtic tol 187, be-w nk cO11t-J c'b181, test WIPGI 181, wo 'kl igcoiita'ct of a 'n'iature .ceii'clucter 147', benk cOht ec't. 14141, test Wi 141 and armature; 126 and its Working; con tact to release trunk c0i1duct0if81" Where. it joins the pi'et ioufly described{hehhng ch"- chit: extending "bitch to the holding inding" of the pitiii' ai'y line switch ljhis holding circuitgnow supplies current to swim-1mg relay 160 of the 'seco'ndai'y line Isxjvitch Q2 the s'witcihhgrlgxy 1- of the 11115 0 selectorv and t-heiholding Winding ,18f0jf thepri? m'ary line switch in i'de'r ,to maintain these relaysenergized. i nce the holding circuit is directly gieunded at the repeater It, vit Will be evident that the lower windi g of the slow acting. release telz'iy'lOl will now be .shortcii'euite d,. It fellows, therefore, that relay 101 is deenergized :nid-fchscoh- Inecte itself ftemthe release tnink'cenductm' 81 at a inetiir e 115.

; contlnui g' new w th the operations ht the iiepezi tei- R, when themelease tigg'nk coiidu ctoi' 187 iS'gIT211ndQC1, a, circuit is closed through the right-hand inding it the shunt field relay 1. O ingtethe factthat th'e je.

'is a closed magnetic circiiit thtough the left harid cote Of this 'rela x the flux is Ch,- yerted fi'oiiiitheeiniethie and the re? layl i si'nbt operated at this time. Infadditioh t0, g'rouridiii the release trunk c61 1; gl uctor. .187 the. elem? acting relay 201 pie erm t; cii'chit foi: .i e1ay20-3 at armature 2 O8 eiid atfz CHIIEIIUJI'Q 209 cibees 'a eii'cuit itch actiiig i'elny 202. Up0n ei1e1ii es tzthliehes a ,lockiiig I ISGlif-tl-h21,11113'61116211. Still 1 1iie s ilt f fthe iieiigi zetien o'f i'elay' 201 1st e ,c l qsiir e Che bridge tcrbss the'coirduc tots 230 2320f thetyunkjliiiejieigtendi iii fl til ifidexchange nd 111m; e niihe ing iiijtheincdihir g .seiecteig This bridge it-4y he ti acedlfi'eih, cenductoi' 2 30 yevey -cfthe u pjj right-hand} winding 01 'the ie peztting coil, the iB'fh hHDd Windiiig tehi etfi l i e ei 1- '0 the l r r ght-c te ground to ceiidiicgripe "111e ch me ten 231.

.; The, celling'suheci'ihef now operate 261 aiid at.

his cellin device-il I accordance With the nekt die; ii-the idesirectiiumber, thereby p zecluc ngr three nterruptions 1n the circuit of the line relay 200 of the repeater R. In response to these interruptions of its circuit, relay 200 deenergizes momentarily three times and at each deenergization transmits a current impulse through the lower winding of relay 203. The operation of relay 203 at this time, however, is of no par ticular effect. In addition, the line relay 200 opens the bridge across the trunk conductors 230 and 232 three times at armature 207, whereby three interruptions are produced in the circuit of the line relay 250 of the selector E. In response to these interruptions of its circuit the line relay 250 deenergizes three times and at each dcenergization closes a circuit for the vertical magnet 256 in series with the slow acting series relay 252. By the operation of the vertical magnet the selector shaft is raised three steps and the wipers 280, 281, and 282 are brought to rest opposite the third level of bank contacts. Relay 252 is energized in series with the vertical magnet and being slow acting retains its armature attracted during the vertical operation of the switch. At the first vertical step the oil normal springs 259 are closed and since relay 252 is now in operated position a circuit is closed through the stepping relay 254. Upon energizing, relay 254 establishes a locking circuit for itself at its upper armature and at its lower armature prepares a circuit for the rotary magnet 257.

At the end of the vertical movement of the switch. theslow acting relay 252 is deenergized and closes a circuit for the rotary magnet 257, which is accordingly operated to rotate the switch shaft one step and bring the switch wipers into engagement with the first set of bank contacts in the level opposite which they are raised. At the same time the rotary magnet breaks the locking circuit of the stepping'relay 254, and this relay is deenergized to open the circuit of the rotary magnet, which then deenergizes also and again closes its interrupter contact. The usual trunk selecting operation is thus initiated, and in case the test contact asso-. ciated with the first trunk line is grounded the trunk selecting operation will continue automatically, the stepping relay 254 and the rotary magnet 257 being energized alternately to advance the switch wipers step by step as long as the test wiper 281 continues to engage grounded test contacts. When the wipers arrive at an idle trunk line, which we will assume to be the trunk line extending to the connector H, Fig. 4, the test wiper 281 will find no ground potential on the test contact 284, the stepping relay 254 cannot again be energized and rotation of the switch will cease. The switching relay 255, which has heretofore been short circuited, is now energized over a circuit extending from the grounded conductor 231, through the winding of said switching relay 255 and by way of the interrupter contact of the rotary magnet, the off normal springs259, and the winding of the stepping relay 254 to battery. Upon energizing, relay the grounded conductor 231 to the test wiper 281 at armature 265 in order to make the selected trunk line busy at once, and at armature 266 closes a circuit through the upper winding of relay 253. Relay 253 is accordingly energized and at armature 269 connects its lower winding with conductor 231, the said winding being, however,esh0rt circuited for the present by the ground at armature 262 of relay 251. In addition to the foregoing, at armatures 264 and 267 switching relay 255 disconnects the incoming trunk conductors 230 and 232 from the winding of the line relay 250 and extends them by way of wipers 280 and 282, bank contacts 283 and 285, conductors 286 and 288 and normally closed contact springs of the reversing relay 307 to the upper and lower windings of the line relay 300 of the connector H. At the selector E when the line relay 250 is disconnected, as explained, it falls back at once and breaks the circuit of the slow acting release relay 251 which deenergizes also an instant later. At its upper armature relay 251 breaks the circuit through the upper winding of relay 253, and at armature 262 it removes the short circuit from the lower winding of said relay. By reason-of the latter operation, in case the release trunk conductor 287 has not yet been grounded at the connector H, ground potential will be supplied to the conductor 231 through the lower windingol relay 253, and relays 253 and 255 will be held locked in a local circuit. As soon as the line and release relays 300 and 301 of the connector H pull up, due to the extension of the calling line to the trunk conductors 286 and 288, the latter relay connects ground to the conductor 287 at armature 312 and the lower winding of relay 253 is short cir- 255 connects lot! cuited. It will be evident then that relay 253 will be deenergized, similar to the way in which relay 1010f the selector D deenergized, and will disconnect itself from conductor 231 by retracting armature 269.

The connection has now been extended asv far as the'connector H, Fig. 4, and the calling subscriber may proceed to call the re malning two digits in the desired number.

newness circuit: From the grounded "armature 3'11 byway of therestin'g contact ofsaid arma tu're,'a'rmature 3'13 and its working contact,

off normal springs 328 and 340, winding of the slow acting v series relay 302, and the winding of the vertical magnet 308. to' bat 'tery, Bythe' operation of'th'e vertical magnet'the switch shaft is raised step by step until the wipers 350, 351 -352, and 353 stand opposite the fourth level of bank contacts.

Relay 302 is energized in series'with the.

vertical magnet and' being slowfacting retains its armature in {operated position while impulses are being transmittedito the yertical magnet. the attraction of armature 314 against its lro nt contact, relay 302 maintains the vertical magnetc'ircuit closed notwithstan'dingthe shifting of the offnor mal springs, which occurs at the first vertical step of the switch. At the en'clrof the vertical movement of the "switch therelay.

302 is cleenergizedahd transfers the operating circuit to the rotary magnet 309.

When the calling subscriber operates his calling device for the ne'zitdigit, which 'is thedigit 5, five interruptions are produced in the circuit ol the linerelay 2000f the repeater R which are repeated as before into the circuit of the line relay 300 oit the 'conjnector H. This time, however; the line relay 300transmits a Series of impulses to the rotary magnet 309 fover a circuit which may be traced as follows From'grounded' armature 311 by way of the resting contact of said armature, armature 313 and} working cont-act, off normal springs 328 and 329,

armature 314 and its resting Contact; arma ture 319 and its resting contact, armature 325 and its resting contact, and the-winding of the rotary magnet 309 to battery- By'the operation of the mmi-y-nngnet the switch shaft is rotated live steps andfthe switch I wipers are brought to rest in engagementwith the particular set ofba nk' contacts in which the line of substati'on'A is termin'ated, these bankcontacts-being indicated" by the reference numerals 354,, 355,356, and

357. The slow acting relay 305' is energized in parallel-with the rotary magnet 309 while the switch is rotating, and atarniature 321 connects the test wiper 352 with testrjelay- 304. Atthe same time relay 305 closes a" shunt circuitaround break contact at -arnia ture 319 of the test relay; at its armature 322,

and thus avoids any possibility-of the" rotary magnet circuit being opened by the opera? tion Off the test relay in case the test-Wiper 352 should engage a grounded contact while the switch rotating. At the end of the rotary movement'of the switch slow acting "relay 305 will de'energizmdan d the further operation at the connector will depend upon whether the line of substation A; is busy or not.

, Assuming first that the" line: is when the test wiii'er 352 engages the test contact 356 it finds aground potential on said t e-fit contactandthetest relay 30 1 will be energized. Upon energizing, relay 304 prepares, allockin-g circuitfor itself atv'arn'iature 318', which is completed as soon as the slow acting relay 305 deenergizes an: instant later.

At its armature 319 relay-30 ktransfers-the operating circuit from they rotary inagnet 309 by way oft-he fourth wiper 351 and associated banlc'contact 355 to the meterC,

associated with .theline of substation "-A and at armatureu320 connects a liead iiroin o the busy signalling machine to theilower side of the trunk line. By the latter opera-f so tion, the calling subscriber is given anaudi- 1 blie busy signal in the usualqmanneirto ad- 7' vise him that-athe; desired line is engagedi I Upon hanging up 'l is irec'eiverlthe calling su-liscriber will; release allot the automatic:

switch-es, but the full explanation of these;

releasing;operations will-be deferred until 3 late/1a; t will be convenient to explain-at deenergizationofthe slow acting 1 '.el'ease relay 301. which falls backan? instant after the line relay 300 and closes the circuit of re lease m'agnet 3 10 in; order to release the con-v nector Eswitch; 1 'Meters, such as theimeter C, are provided for certain"subscribers lines wl'ie 'n called for in order to;registeritheinulnrv ber. of times suchsubscribersarecalled when busy. I

It willl be assumed now thatlthe, line of substation A was idlei when called, as described in the foregoing and the establish;- mentof-the connection will; he; proceeded with. ,Und'er'the assumption that the line is inidle condition the test: Contact 356 will not be grounded and when the line is con necte'd'withbythe connector H, the test. re- 121511 304'will not be energized. Then, when the'slowacting relay 305 falls back an in.

stant later a circuit completed for. the

switching relay"306 which "extends as follows: From ground at armature *3l2iby way of conductor 346, armature 318 and'its rest I ing 1 Contact, upper winding of the switching relay 306, resting contact of armature, 321 and th'esaid armature, test wiper 352, test contact 356', private i'iorr'n'al conductor 3Y1,

twiiiding ofthc switching relay 360 ofthe linle switch? and the winding oftheifstep 7;

ping magnet- 361- to; battery. Upo'nthc closure of this circuit relays 306 and; 360 are energized :in series and the latter relay disconnects the line conductors37.0-a1id 7372: or

of the linev extending to suhstaticn, Ao from LII the winding of the line relay 362 and from ground, respectively. By reason of a mechanical interlocking device controlled by the armature otline relay 362, the armature of the switching relay 360 is operated only about half way, and the wipers of the line switch are not connected up.

At the connector H, when the switching relay 306 is energized it establishes a locking circuit for itself at armature 326, opens the rotary magnet circuit at armature 325, connects direct ground to the test wiper 352 at armature 324, disconnects the condenser 347 from in bridge of the line relay 300 at armature 348 and at armatures 323 and 327 connects up the line wipers 350 and 353. By the latter operation a signalling circuit is completed over which ringing current from the generator GEN is projected to operate the bridged ringer at substation A, thereby notifying the subscriber that he is wanted at the telephone. The upper winding of the ring cut-otl' relay 303 is included in the signalling circuit, and when the called party r-esponds by removing his receiver the said ring cut-oft relay is operated, establishing alocking circuit for itself at its armature 316. In addition, the ring cut-oil relay 303 breaks the ringing circuit at armatures 315 and 317 and at the working contacts of these same armatures finally completes the talking circuit. The transmitter at substation A" is now supplied with talking current through the windings of the double wound back bridge relay 307 which is accordingly energized and reverses the incoming trunk conductors 286 and 288 as regards their connection to the windings of the line relay 300. This operation reverses the "direction of current flow over trunk conductors 230 and 232, and also, therefore, the direction of current flow through the left-hand winding of the shunt field relay 1 at the repeater B. This winding, which is included in the circuit of the line relay, is normally energized so that the polarity of the associated left-hand magnet core is opposed in sign to the polarity of the right-hand core; that is, it the upper end of the right-hand core is positive, the upper end of the left-hand core willvbe negative. Thus, under normal conditions before the called party answers the magnetic flux gener v ated will flow through the two magnet cores in series and will not effect the armature of the relay. lVhen the current in the left-hand winding is reversed, however, the polarity of the left-hand core is reversed also, and the magnetic flux produced will necessarily flow through the two cores of the magnet in parallel and through the armature of the magnet and the heel piece (not shown). Accordingly the armature is attracted and a circuit is completed for the reversing relay 205, which is at once energized in order to reverse the direction of current flow in the trunk conductors 186 and 188 and in the calling subsc'ribers line. These reversing oper tions although of no particularutility in connection with the apparatus shown herein,

are required on occasion forthe purpose oi,

operating a meter, or other device, and since they are ordinarily provided for in working this relay accordingly deenergizes and breaks the circuit of the slow acting release relay 201 and also opens the bridge across the trunk conductors 230 and 232 at armature 207." By the latter operation the circuit of the line relay 300 of the, connector H is broken and relays 300 and 301 deenergize to cause the release of the connector H, as has already been briefly explained. It will be understood, of course, that during the release of a successtul connectlon the meter C 1s not I operated, due to the fact that the test relay 1 is not energized. The release relay 301 also disconnects ground from release trunk conductor 287, thereby breaking the holding circuit of the switching relay 255 of the selector E. Upon the deenergization of the switching relay 255 the selector E is restored to normal through the medium of the release magnet 258. 2 I

Returning to the repeater R, when the line relay 200 falls back it also closes a circuit through the lower winding of relay 203, which is accordingly energized to disconnect ground from the release trunk conductor 187 at armature 217 and to open the'locking circuit of relay 202 at armature 212. .An instant later relay 201 doenergizes and breaks the initial energizing circuit of relay 202 at armature 209, breaks the energizing circuit of relay 203 at armature 208, and 'immedi ately closes an alternative energizing circuit for relay 203 at the resting contact of armature 210. Relay 202 being slow acting remains in operated position for an instant after its circuit is broken at armature 209 and maintains the previously mentionedenis released also.

lease of the connector Hit retains relay 203 in operated position. until, the slow acting relay 202 falls back anddisconnectsit from in'bridge of the trunk, conductors 230 and 232. The release of the secondary line switch S the selector 1), and the primary and secondaryline sw tches P and S, occurs when ground is removed from therelease trunk conductor 18?- hy the deenergization of slow acting release relay 201. .When

ground is removed from release trunk con-,

ductor 187, relays 1 and 104015 the sec ondary line switch S and the selector D,

respectively, and the holding-windinglS ot' the primary line switch P are deenergized and these switches are restored in the well known manner, the selector D being returned to normal by the operation of the release magnet .07.. 1 When theprimary line switch P withdraws its plunger fromythe bank, ground is disconnected from conductor 51, whereupon the secondary line] switch S Having described theordiiiary operation of the system it will be convenient now to describe certain ot thefeatures of thein-g vention more in detail, and to callatten'tion to certain other features which 'couldnot readily be explained while describing the es tablishment ofan ordinary connection. T he eidentallyprovides tor -locking up the connecti'onl whenever an open trunk line is ens countered, Considering the primary lineswitch P, Fig. 1, it has been customary to make the line relay. of a line switch of this character slow acting by ineans of a copper slug in. order to enable it to holdthe pull down winding energized until ground is fed back over therele ase trunk conductor from the first selector,

' are difli'cult to, adjust, since they are only energized for an instant and consequently do not become fully saturated, which makes it hard to obtain the desired slow releasing The locking arrangement characteristic, forthe linerelay of a switch of this type, such as, is shown for the line relay 1 6 of the lineswitch P,entirely eliminates allot the trouble heretofore encountered due tothe I present inventionis connected byiway ofa use of the slow acting line relays. J

V Thiscircuit arrangement also 1 iti.OClUCGS a decided advantage in the case ottheplunger, type secondary line switches, such as the line switch S, Fig. 1. It hasbeeninecessary heretofore to provide aylin'e switchof this type with a low resistance slow acting relay,

included in the open main conductor 62, orrather in the branch thereofwhichis indie vidual to the line switch, which relay when energized connects ground tothe release These slow acting line relays.

rary holding circuit for retaining the pmniary l ne switch n operated position until "trunk conductor 52, thus providing a tempo I the relays in the first selector have had time 1 to energize. It will be clear that the present circuit arrangement renders the relay re ferred to entirely unnecessary, and the secondary line switch as shown-in the drawing requires only a single core having the pull down and holding windings as illustrated.

encountered, it will be clear that when a call is made from the substation A, as described in the foregoing pages,'if one of the con- Considering now the feature of locking the connection n case anopen trunk lineiis.

ductors of the trunk lineextending tothe secondary line switch S is open, or if one of.

the conductors of the trunk line extei'iding to the firstselector Dis open, or it either of these switches or the primary line switch failslto function properly, the release trunk conductor 52 will not be grounded at the first selector switch, the lower winding of the l ne relay 16 will not be short circuited,:

and this relay will, therefore, remain locked up, The locking c rcuit includes the COII1.-

inon conductor"25 and the left-hand winds: ing of'supervisoryrelay 39'wli1ch is operated also to light the supervisoryla np L.

This lamp is provided to, attract the attention of a switch-board'atten dant who, will 7 I immediately proceed to investigate the troua bleand correetit. fl f'desire'dan audible alarm} ct -somekind can beoperated at the same time; as the lamp. L in any convenient orsuitablemanner... It:will be appreciated that the arrangement described provider an effective niethod of' locating trouble speedily and surely, while at the same time the annoyance to thesubscribers concerned is reduced to a minimuin,for the attendant when notified ofy a case of trouble is able at the same time to ascertain the number of the subscriherwho has met with difiiculty andcanreassure or assisthim in getting his number hefore he has had time toiii ak'e a,

complaint.

The locking circuit for the line relay or a line switch is also applicable to line switches of tlierotary type, as will be seen by referring to the circuit of line switch P, Fig; 4, Considering the line relay 362 of this switch, the armature 866, which ordinarily is connected to ground, according. to the common conductor through the low resistance supervisory relay 365 to ground, and axlowv resistance locking winding is substnv tutegd for theusual copper slug. The operation so far as the nvention s concerned is identical Wltli the operation described in selected, this relayand the-line relay remain locked up in series with the supervisory relay 365 until ground is fed back from the first selector .over the release trunk conductor, such as the conductor 381 of the selected trunk line, which operation will -ttentioie may now he directed to thenia'nn'er in which the locking feature is applied to the lirst selector D. It will be recollected that when the selector D establishes connection with an idle trunk line and the switching relay 101- operates, ground is supplied to the release trunk conductor 81 through the 'lower'low resistance winding of the release relay 101, said relay remaining locked up until ground is connected to the release trunk conductor 187 at the repeater R. If either of the trunk lines beyend the selector D is defective to an extent which makes it inoperative the release trunk conductor 1 17 will not be grounded and since the lower winding of relay 101 will not be short circuited the connection will remain locked up. Switching relay 1 when it energizescloses a circuit for the lamp L at armature 127. If the apparatus functions properly relay 101 will deenergize an instant later and will open this circuit atarmature 116, but if relay 101 fails to deenergize, as is the case when a defective trunk line is encountered, lamp L will remain lighted to signal the attendant. The pilot relay 130 may be common to a plurality of lamps, such as the lamp L, and can be used to sound an audible alarm if desired.

As in the case of the local secondary line switch S, a decided advantage is also intro duced in the case of the outgoing secondary line s vitch S Heretofore an outgoing secondary line switch of this type has been provided with a slow acting line relay, instead of an ordinary quick relay like the line relay 101. This slow acting relay was provided with spring contacts for grounding a release trunk conductor, such as conductor let-7, in order to maintain the preceding selec tor switch in operated position until ground could be fed back from the repeater in the trunk line to which the connection was eX- tended.

It will be clear that when a selector such" as the selector 1) is'used, which feeds ground forward over the release trunk, this arrangement in the outgoing secondary line switch is entirely unnecessary. As shown in the drawing ofthe line switch S Fig 2, no slow acting relays whatever are used for controlling the ordinary operation of the selector and it has been found desirable to do this in some cases. The operation of relay 253 will be sufliciently understood from whatjhas been said to make itunnecessary to go into further details, but it may be mentioned that in case the selector E becomes locked on an open trunk, the relay 253 will hold the circuit of the lamp L closed in order to signal the switch-board attendant.

Referring now to the repeater R shown in Fig. 3, the circuit of this switching mecha nism is also arranged in a special manner to take care of trouble due to open trunk lines. In this case, however, as the circuits are ordinarily intended to operate, if' the outgoing trunk line from the repeater is open, the connection from the calling sub scribe]: will not be locked up as in the preceding cases, but Wlll bedisconnectedwhen the calling subscriber hangs up. The trunk line,

however, extending to the repeater R will be,

made busy,- so as to prevent other calling subscribers from obtaining access to it. The manner in which this is done may be. de scribed briefly by considering the operation which takes place when the calling subscriber hangs up his receiver after an unsuccessful connection, caused by a defect in thetrunk line comprising conductors 230 and 232.

lVhen the receiver is replaced the line relay 200 falls back andbreaks the circuit of the release relay 201, at the same time closing a circuit for relay 203, which energizes to open the locking circuit of relay 202. After an instant the release relay 201 falls back, removes ground from the release trunk conductor 187 in order to release the preceding switches, breaks the circuit of relay 202, also the circuit of relay 203, andfinally closes the upper winding of the latter relay in bridge of the trunk conductors 230 and 232. In the event the trunk line is in operative condition, relay 203 will be held energized by means of its upper winding and the slow acting relay 202 will become unlocked, but in the present case since the trunk line is assumed to be open relay 203 will fall back immediately, and will close the locking circuit of relay 202 before the said relay has time to fall back. The release trunk conductor 187 is now connected to ground by way of armatures 214C and 217, rendering the trunk line busy. In addition, since. the

but in the'case of the selector D the circuit arrangement is such that this make-before break contact spring arrangement can be used to good advantage and without introducing any trouble.

The operations which take place at the se lector D iii-case a leaky line, or a line having a high resistance short circuit across it, is extended to the selector will now be explained. Certain details of the winding and mounting of the relays 100, 101, and 102 should first be explained, however, in order i the center, as shown, this relay is in a position to influence and be influenced by the other relays to some extent. This effect is enhanced if the line relay is provided with a brass heel piece, which greatly increases the leakage of the magnetic flux. These three relaysare wound in such directions that if the armature end of the line relay 100 is a north pole, for example, the armature end of the relays 101 and 102 will both be south poles. \Vih this explanation the operations which take place when a line develops a short circuit high enough to operate the primary line switch and is extended to the first selector D will be understood. l/Vhen the selector D is connected with, the line relay 100 is energized just. enough, we will say, to cause armature 112 to engage contact spring 110, at which time the tension of spring 110 begins to resist the attraction of the armature and prevents further movement thereof for the time being. With armature 112 in engagement with spring 110, a circuit is completed for the release relay 101 which is energized and at armature 113 closes a circuit for the vertical magnet 105. Since the leakage flux produced by the energization of release relay 101 is in such a direction that it tends to build up the magnetism in the line relay 100, the line relay may now be sufficiently energized to completely attract its armature. At any rate, whether the line relay is completely energized at this time or not, the leakage flux due to the energization of the release relay 101 assists the energization of the line relay 100 instead of opposing it, and the establishment of a buzzer action between these two relays, such as would be apt to occur if the release relay were wound in the opposite direction, is prevented- Assuming then that the line relay 100 merely energizes su'lficiently to close the three contact springs together, when the vertical magnet operates the shaft is raised one step and off normal springs 122 and 123 are closed. This completes a circuit for relay 102, and also a an cuit for relay 10S; Relay 103, upon enermagnet circuit at armature 118. The selector now operates to select an idle trunk line on the first level in theordinary manner. As suming that the trunk line terminating in bank contacts 150, 152, and 153, and comprising conductors 15 1, 155, and 156 is selected, the defective subscribcrs line is extended to an operators position, the operators equip ment in which the trunk line terminates being shown immediately above the secondary line switch S in Fig. 2. Theline relay which is bridgedacross this trunk line preferably has a weak adjustment and is accordingly energized, followed by the energization of the associated release relay which lights the lamp to attract the attention of the operator. It willbe noticed that there is no provision made for grounding the release trunk conductor 155 in the ordinary course of events and it follows, therefore, that any connection which is cxtended'to the operators position by way of the trunk line in question will be locked up, since the lower winding of the release relay 101 will not be short circuited or deenergized. The operator may answer the call by throwing her listening key and in case there is a subscriber on the line who has called in on the first level by mistake,.she.

can actuate the key K which will ground the release trunk conductor 155 and place the circuits in such a condition that the subscriber can. release the connection. Other wise the operator will notify the switchboard attendant, who will proceed to trace back the call and ascertain the number of the line which is in trouble in order that the short circuit may be cleared. Although in the foregoing explanation a line having a high resistance short circuit has been nie'ii-' tioned, it will be apparent that a line having a high resistance ground on the negative side will be automatically extended to the operator in the same way.

The leakage flux between the cores of the line relaylOO and the relay 102 also has a pronounced effect on the latter relay in its ordinar 7 operation, as will now be pointed out. Although the circuit of relay 102 is closed as soon as the switch shaft begins to rise, this relay is of very high resistance and impedance, as explained hereinbefore, and does not energize until the vertical movement is completed, at which time the line relay 100 comes to rest in energized position. At this time it is desirable that relay 102 should pull up instantly in order to set-1 *s' at iinpirlse's, the niagiietic fluxint-heline relay builds up rapidly until therelay bec'oi'iies'satur'ated and aco'nsiderable leakage flux'win now be produced 'which'will 'efi'ect the any-102 in properi'nan'ner to hasten H Li ' fall back more its energization.

The scheme of so arrangingtlie polarity of the l1ne, 'rlelease, andseries relays so as to assist in the operation e fthe switch can also be applied to, an nary selector, such as the selector .13, F1 111- wh'rehfiswitch it is I, I, \H7 availed it to nnprovethe operation oi the.

25O'by causing the said relay to quickly when its circuitis broken and to pun up More quickly whenits circuit is'c'l'osetl: 'Inthisfselector circuit the relays should be so wound that if the arniatut-e end oi the line r'elafi is the north pole, I for 'eXa1nple,"the ariiiature end of the release relay 251 willalso be a north pole, While the all'll atul' e end ofth'e series relay 252 will be a south pole; The relaypolarities are indicated in nnedia'tely below the circuit diagram' oi the selector E, Fig; 3." Considering the operation of the switch in order to explain how the o1f3er'a-tion of'the' line relay-250 is 'in i- )io\'*etl, when' the line relay is energized it closes a; circui't'for therel-ease relay 2:51, and the leakage flux produced by the energizertionfo-f-tlie latt r relay will oppose the flux tl'nou'gh the core of the line relay; consequently when the circuit of thefline relay is broken it will deen'ergize rnorefquickly than would otherwise be thec'ase. hand, when the circuit 01 the line relay 250 is again closed after the first interruption the energization of release relay 251 is ataniin'imum, but series relay 252 is fully'energized and the polarity of this relay is such that the leakage flux produced by its energization tendsto assist in the magnetization of the core of-t'h'e line relay: It will be seen, therefore, J

said release relayan'd cause it to deenergize.

that :by properly arranging the windings of the-three relays mentioned, so as to produce proper polarities, vthe operation of the line relay can be considerably improved. 7'

Having described m invention, what I consider to be new" and desire to have prot'ected by LettersPatentawillbe pointed out inthe appended elai-msp J a 1 hat Icclairn as my in'vention'is'z' .i 1-; In an; automatic telephone system, two seriaflly' relateclautomatic switches for con meeting calling and. called lineya trunk I'i-iith the "polarity of the relays as On the other "line extending betweensaid switchesinolud 1n a release trunk'conductoaineans in the first switch for selecting'said trunk line and for grounding said contlnctor when the trunk s connected with, ineans 1n the'second switch ior ground ng said conductor thereaiterjzmd means in first switch responsive ing release relay in said selector switch, and

means con-trolled over said trunk line for short icireuiting the locking winding of said relay over a conductor of said-trunk line to cause it to deeiiergize;

3. In. a telephonesysteni, atrunk line, a selector switch and ni'eansfor 'operatingit to Connect with'said trunk line, a self locking" release relay in. said sele etor switc h, another swltch-in which said trunk line terminates, a

line relay: in. the said other switch energized over the trunk line when thesame is connected with, and means controlled by said line relay for grounding a conductor j of f said trunk line to short circuit-the locking winding of said release relay to cause the said relayto deenergiz e. e

, 4. Li telephonesysteni, a group era-uni: lines, a' release trunk conductor, .eachtrunk li1ie, an automatic switch and means for operating it to connect with an idle trunk line,'a release relay in said switch lockedin e-neip'iae'd position w i'entheconnection is established, and ineanscontrolled over the selected trunk line fo'rgronnding the release 'truhlr conductor thereof to unlock said relay.

I i Iii a telephone system, a gron i e'ftrunlr v lines, a release trunk conductor in each trunk .line' an. automatic switch and means for 0 rating it to connect with an idle trunk line, a releasetrunkconductorincoming to saitlselector, means for connecting the said incoming release trunk conductor with the release trunk conductor of the selected trunk line when suchtrun'k'line is connected with,

a' lrelea'sje relay and a winding therefor supplying; current to said incoming release trunk conductor, and means for connecting a cur rent source to the release trunk conductor of the connected trunk line to short circuit feontrolling the operation 'of the switch,

means for changin saidflrelease relay to a quick acting relay when the trunk is cm,

nected with, and a locking circuit for holding sa'id release relay energized after its I character is'-changed.' y 7 I 72 111 a telephone systent a trunk line, a

selector switch and means for operating it to connect with said trunk line, a quick act ing line relay and a slow acting release relay controlling the operation ot said switch, a switching relay "for completing the connection to said trunk line, means controlled by said switching relay for changing the re lease relay to a quick acting relay, a holding circuit for said switching relay completed over said trunk line after the same is connected with, and a locking circuit for maintaining said release relay energized until said holding circuit is established.

8. In a telephone system, a trunk line, a selector switch and means for operating it to connect with said trunk line, a quick acting line relay and a slow acting release relay controlling the operation of the switch, means for changing said release relay to a quick acting relay when the trunk is con nected with, a locking circuit for holding said release relay energized after its character is changed, and means associated with the said trunk line for unlocking said release relay provided the trunk line is in operative condition. 1

9. In a telephone system, a trunk line, a selector switch and means tor operating it to connect with said'trunk line, a self locking release relay in said selector switch, and means for unlocking said relay contingent on said trunk line being in normal operative condition when connected with.

10. In a telephone system, a trunk line, a selector switch and means for operating it to connect with said trunk line, a sell: locking release relay in said selector switch, means for unlocking said relay only in case the said trunk line is in operative condition when connected with, and means for signalling an attendant if the relay is not unlocked.

11. In a telephone system, a subseribers individual line switch, a trunk line, subscriber controlled means including a line relay for operating said switch to extend a connection over said trunk line, means for establishing a holding circuit over said trunk line to maintain said switch in operated posi tion, means for disconnecting the line relay when the connection is extended, and a looking circuit for maintaining said line relay energized until said holding circuit is established.

12. In a telephone system, a subscribers individual line switch, a trunk line, subscriber controlled means including a line relay for operating said switch to extend a connection over said trunk line, means for establishing a holding circuit over said trunk line to maintain said switch in operated position, means for disconnecting the line relay when the connection is extended, a locking circuit for maintaining said line relay energized until said holding circuit is established, and aconnection between the said locking neraeee circuit and holding circuit, whereby the said line relay is short circuited and deenergized when the holding circuit. is established.

13. In an automatic telephone system, three serially related automatic switches for connecting a calling and called line, a release trunk conductor extending through all three of said switches after the connection is established, means for grounding said conductor in the first switch when the connection is eX- tended to the second switch, means for grounding said conductor in the third switch when the connection is extended to the third switch, and means in the first switch responsive to the grounding of said conductor at the third switch tor removing the ground at. the first switch.

14.111 a telephone system, three serially related switches for extending a calling telephone line, a line relayin the first switch, means in the first two switches responsive to the energization of said line relay for operating said switches to extend the calling line to said third switch, means for disconnecting said line relay when the first switch is operated, means in the said third switch tor completing a holding circuit to maintain the first two switches in operated position, and a locking circuit for maintaining said linerelay energized until the said holding circuit is established.

v15. In a telephone system, three serially related switches for extending a calling telephone line, a line relay in the first switch,

means in the first two switches responsive to the energization of said line relay for 0peratmg said switches toextend the calling line to said third switch, means for d1scon necting said line relay when the first switch' is operated, means in the said third switch for completing a holding circuit to maintain the first two switches in operated position, a locking circuit for maintaining said line relay energized until the said holding cir cuit established, and a connection between the locking circuit and the holding circuit for shortcircuiting the locking winding of said line relay to deenergize the same.

16. In a telephone system, a selector switch and a repeater for connecting a calling and a called line, a rotary secondary line switch inserted between said selector switch and said repeater, a switching relay in said secondary switch for closing the talking conductors, a circuit for said switching relay maintained closed at the selector switch, means for closing said circuit at the repeater, and means for then opening said circuit at the said selector switch.

17. Ina telephone system, a selector switch and a repeater for connecting a calling and a called line, a rotary secondary line switch inserted between said selector switch and said repeater, a switching relay in said secondary switch for closing the talking conductois; a release trunk conductor extending tllrotigh hothof said syyitches to said 1 repeater, a connection fr'oni said conductorto sa'l switching relay to hold it energized, 1n ari'sffor" grounding the said conductor-in t'liief sele'ctor switchinclnding a release relay havinga locking Winding included in the ground connection, and-means for ground mg the stud eondu'ctor in'the said repeater,

{therebysaid release i'el'a'y is'short ci'lCll' and deenergized;

18. It'll an automatic telephone system,'

ineans for connecting a calling andfcalled lifn'e incluc'ling a'r'e 'oeater and outgoing trunk line and anantolnatic switch intervening between the callingjline and said repeaterya manually operable key associated Wltlr' said 1 arrangements cooperating position the'saifd switch cannot'be released by the calling subscriber in case the trunk lineis open, While with the key in the other position the calling subs riber, can release the sai'c'lfswyfitch, and in'e'ansfor making the repeater and trunk line hn'sy after the'sWitch has been released. L V 19. In s an autoin tic tele'p'hone system, means for cion'ne' ctlngfa g and called line in'cluding inserial relation an auto Inatic switch", arepeateaan-d. an" outgoing,

t'r'unk line, nieansfor preventing the calling subscriberfroin releasing the said switch in case the said trnnk line is open a signal, and means for o-perati'ng' said signal in case the calling subscriber attempts 'toi'release said switc'hand is prevented fromjdoi n'g'so} 20. In. .an automatic" telephone. system," a series of trunk lines and assoeiated autoi'na'tic' switches for conn'ecti'nga calling and called line,a controlling line relay for each switchhridged across the associated" trunk line in series with the exchangebatt ry-,a condenser connected in brrdgeof eafch trunk line at the terminals of the associated 11116 relay, and means for disco 'inecting each eou denser and line relay v after the associated switch is operated.

21f. Infan automatictelephone-system, ser-i lly relatedlselectorxswitches and conn'QC If switch for connecting a caning and called line, interconnecting trunk lines there beinga trunk line terminating in eachflolf said styit'ches, .a eontrolling line relay for each switch bridged across" the associated trunk line in" series with the exchangebattery, a condenser bridged across eaeh-triinli lineat the terminals of the associated; line i-elay.frne'ans fordisconnecting? the condenser and line relay from the trunk lineat each selector switch "after such selector is operated, and means for'fdisonnecting"the eondenser the connect-or after itflhas' been operatedgthe line relay atj the c'o'rinectdi" being retained-inbridge ofthe associated trunk line to supply talking current to the calling line.

1 that with the key in one 22! In an antennae; telephbne system; a selector switch having primaryand secondinci ement, a line 'circnit', a line relalf re- 1 sponsrve to moment ry interruptions o' the 'e cn'- 1:1;1tfor ansmg the pirrmary ino vespo'n's'lve only to prolonged .closufreiof' the line" circuit folloa 'ingfone me e; mginen-- tar-y 'lnaerrtiptions thereof fer-"swung" the secondary lnoven'lent" 23 111* an" automatic telephone system, a selecto swi-tch having primary and secondary movement, a quick acting line relay and a; Slow" acting release relay for controlling th OjlQ Q fi Iti n and release oflthe' switeh', a relay for controlling the change over from prin'iary tOJ SGCO'D'ClaIY movement, and a cir-'- cnit the change oyer' relay 'closed hy the line relay each "time itis energized after the first'deen'ergfization dufrihg a s'eri'es of pulses, the said change over relay having a windin of high resistance and impedance and being adjusted so that will not operate 7 until the line relay comes tot rest in, energiZed' position after the series of "impulses spon'sive to inonientar'y' interrupt-ionsof the hn circu t for causing the'prnna ry move-'1 Tentfof 'said switch, a se'cond relay i or starting the secondary movement mounted adja' cent said line relay,- a circuit for said sec- "ond; 'r'elay closed by saidjlinje relay after the first deenergi'zationthereof, said second relay heingres 'aonsiye only to a prolonged energiza'ti'on of the said line relay following on ormoredeener grzanons thereof, and the saidrelay's being wonnd'so that the leakage flux resulting fromthe p'lolonged energiza tron o f the line relay assists 1n the energizaassists in 'ene'rg iz'ingthe said sec- Inn tion. ofth'e secondrelay'and causes the lattel-ta operate morerapidly. Q r

2 6 In automatic telephone syste'rn'fa selector switch having all-me relay, means" for automatically extending a-snb'scribersline: which is in troubleto the line relay of said "selector; and, circuit arrangements in the selejc't-Qr's'uch that in case-the line relay is not-full energized the selector will operate automatically to extend the line which is in trouhletdafi operators position;

27. In an automatic telephone systerii', a selector switch having primary andsecondary movements and a controlling line relay, means responsive to a complete energization of said relay and momentary deenergizations thereof for causing the primary movement, means for starting the secondary movement when the deenergizations cease, and circuit arrangements such that a partial energization of the said line relay will cause a definite primary movement followed automatically by a secondary movement.

28. In an automatic telephone system, a selector switch having a. primary operating magnet and a controlling line relay, a second relay for preparing a circuit for said operating magnet and for controlling the release of the switch, make before break contact springs on said line relay for controlling the primary magnetcircuit and the circuit of said second relay, and other circuit arrangements whereby the said line relay is prevented from permanently closing the circuit of the primary magnet in case said relay is only, partially energized.

29. In an automatic telephone system, a selector switch having a primary operating magnet and a controlling line relay, a slow acting release relay mounted adjacent said line relay, and make before break contact springs on said line relay for controlling the primary magnet circuit and the circuit.

ofsaid release relay, the said relays being wound so that when the release relay circuit isclosed by the line relay the leakage flux produced bythe energization of the release relay assists in the energization of the line relay.

30. In a. telephone system, a selector switch, a quick acting line relay and a slow acting release relay for controlling said switch, said relays being mounted adjacent one another, and means for interrupting the circuit of the line relay to cause the opera tion of the switch, the said relays being wound in such directions that the leakage flux produced by the energization of the release relay assists in deenergizing the line relay when its circuit is interrupted.-

31. In an automatictelephone system, a selector switch and a line circuit extending thereto, a line relay deenergized responsive to interruptions in the line circuit for controlling the primary movement of the switch, and a second relay for starting the secondary movement having a circuit which is closed by the line relav at each deenergizationthereof, said relays being mounted adjacent one another and being wound in such directions that the leakage flux produced by the energization of the-said second relay when the line relay is deenergized responsive to an interruption assists in energizing the line relay when the line circuit is closed following the interruption.

32. In a telephone system, a selector deenergizing the line relay when the line circuit is interrupted, while the leakage flux produced by the energization of the change over relay assists in energizing the linerelay when its circuit is closed.

33. In an automatic switch, two controlling relays, and magnetic cores for said relays each positioned within the magnetic field of the other so that the energization of one relay will affect the operation of the other relay.

34. In an automatic switch, two controling relays mounted adjacent one another and poled so that the leakage flux resulting from the energization of one relay assists in the energization of the other. i

85. In an automatic switch,,three controling relays mounted adjacent one another and poled so that the leakage flux resulting from theenergization of the first relay will assist in the energization of the second and so that the leakage flux resulting fromthe energization of the third will assist in the deenergization of the second.

36. Inan automatic switch, a line relay, a release relay, and a change over relay, the line relay being mounted on the switch close to and between the other two relays and the said relays being so poled thatthe energization and deenergization of the line relay is assisted by the leakage flux resulting from the energization of the change over and re lease-relays, respectively. 7

37. In an automatic switch, a line relay having a non-magnetic heel piece, and another controlling relay having a magnetic heel piece, said relays being mounted each within the magnetic field of the other so that the leakage flux produced bythe energization of one relay affects the operation of the other relay.

38. In a telephone system, a trunk line leading to an operators switchboard, automatic switches for extending a calling line to said trunk line, means for automatically locking up the connection to prevent release by the calling subscriber, and means controlled by the operator for placing the release of the said switches under the control of the calling subscriber.

In witness whereof, I hereunto subscribe my name this 5th day of May, A. 11,1921.

CLARENCE lil. LOMAX. 

